Method for simultaneously washing a plurality of containers

Abstract

This disclosure provides a method for simultaneously cleaning multiple containers, each having an opening and its inner wall coated with reaction residues including polylactic acid oligomers. The method includes: adding a cleaning solvent to each container; connecting each container to a reflux condenser; setting a predetermined cooling cycle temperature for condensation; heating the multiple containers and maintaining the heating for a predetermined time to obtain a mixture containing dissolved reaction residues; and removing the mixture from each container to obtain cleaned containers. This disclosure provides a simple, low-cost, and highly efficient method for simultaneously cleaning multiple containers.

Description

[0001] This application was filed on [date]. November 3, 2022 Application number 202211372631.7, invention title: at the same time Method for cleaning multiple reaction vessels used in the preparation of lactide A divisional application of the patent application. Technical Field

[0002] This disclosure relates to the field of biodegradable polymer materials, and more specifically to a method for cleaning multiple containers simultaneously. Background Technology

[0003] Medical-grade lactide is an important raw material for the synthesis of medical-grade polylactic acid (PLA). Medical-grade PLA possesses excellent biocompatibility and good mechanical properties, and its degradation products are carbon dioxide and water, making it a safe and environmentally friendly medical material. Medical-grade PLA has wide applications in surgical sutures, bone fixation materials, drug delivery systems, and tissue engineering scaffolds.

[0004] There are two main methods for synthesizing polylactic acid (PLA). The first is through condensation reaction, and the second is through ring-opening polymerization of lactide. Because water is difficult to remove from the reaction products of the first method, the resulting PLA has a relatively low molecular weight. Currently, the second method is generally used both domestically and internationally. This involves first obtaining pure lactide through lactic acid condensation and cleavage, and then obtaining medical-grade PLA through ring-opening polymerization of lactide.

[0005] The commonly used method for preparing lactide is a two-step process. Specifically, lactic acid is first directly polycondensed to obtain low-molecular-weight polylactic acid (PLA), which is then pyrolyzed at a higher temperature to generate lactide. In small-scale preparation of medical-grade lactide, flasks are typically used as reaction vessels. The reaction residue is primarily PLA (i.e., PLA oligomers) that cannot be pyrolyzed into lactide. This residue has high viscosity at high temperatures, making it difficult to pour out and posing operational safety risks. After cooling, it solidifies and cannot be poured out. Disposing of the flask directly as hazardous waste results in resource waste and high costs. Summary of the Invention

[0006] This disclosure was made in view of the above-mentioned prior art, and its purpose is to provide a method for cleaning multiple reaction vessels for preparing lactide simultaneously, which is simple, low-cost and highly efficient, as well as a cleaning solvent for cleaning reaction vessels for preparing lactide.

[0007] To this end, the first aspect of this disclosure provides a method for simultaneously cleaning multiple reaction vessels for preparing lactide, comprising the following steps: preparing a cleaning solvent, wherein the cleaning solvent is a potassium hydroxide solution with a concentration of 0.1 mol / L to 1 mol / L; adding the cleaning solvent to each reaction vessel respectively, wherein the ratio of the volume (in L) of the cleaning solvent in each reaction vessel to the mass (in kg) of the reaction residue in each reaction vessel is not less than 1; installing a reflux condenser at the opening of each reaction vessel, and connecting the reflux condensers in series to a condenser; turning on the condenser and setting a predetermined cooling cycle temperature for condensation, heating the multiple reaction vessels until the cleaning solvent inside each reaction vessel reaches a predetermined heating temperature, and maintaining the heating for a predetermined time to obtain a mixture containing the reaction residue, wherein the predetermined heating temperature is not less than 150°C; removing the reflux condenser from the opening of each reaction vessel, removing the mixture from the reaction vessel, and obtaining a cleaned reaction vessel.

[0008] In the first aspect of this disclosure, by using potassium hydroxide solution as the cleaning solvent and configuring the concentration of the potassium hydroxide solution to be between 0.1 mol / L and 1 mol / L, the reaction residue can be dissolved in the alkaline cleaning solvent, thereby improving the cleaning effect of the reaction vessel. By configuring the ratio of the volume (in L) of the cleaning solvent in each reaction vessel to the mass (in kg) of the reaction residue in each reaction vessel to be not less than 1, it is beneficial for the reaction residue to react fully with the cleaning solvent, thereby facilitating the dissolution of the reaction residue. By installing a reflux condenser at the opening of each reaction vessel, the vapor of the cleaning solvent that is subsequently heated and evaporated can be refluxed back into the reaction vessel to participate in the reaction. By connecting the reflux condensers in series with a condenser, it is convenient to reflux the reactants in multiple reaction vessels simultaneously when cleaning the reaction vessels, thereby improving the cleaning efficiency of the reaction vessels and the utilization rate of the equipment. By configuring the predetermined heating temperature to be not less than 150°C, the dissolution rate and solubility of the reaction residue in the cleaning solvent can be increased, thereby improving the cleaning effect of the reaction vessel. Therefore, a method can be provided that is simple, low-cost, and highly efficient, enabling the simultaneous cleaning of multiple reaction vessels used for preparing lactide.

[0009] In the method according to the first aspect of this disclosure, optionally, the predetermined heating temperature is 150°C to 160°C, and the predetermined heating time is 6 hours to 24 hours. In this case, it is beneficial for the reaction residue to react fully with the cleaning solvent, thereby facilitating the full dissolution of the reaction residue in the cleaning solvent and improving the cleaning effect of the reaction vessel.

[0010] In the method disclosed in the first aspect, optionally, the plurality of reaction vessels are heated simultaneously using an oil bath. In this case, by placing the reaction vessels in heat-conducting oil, the bottom region of the reaction vessels can be uniformly heated, which facilitates the complete dissolution of reaction residues in the cleaning solvent, thereby improving the cleaning effect of the reaction vessels.

[0011] In the method according to the first aspect of this disclosure, optionally, the number of the plurality of reaction vessels is two to four. In this case, two to four reaction vessels can be cleaned simultaneously.

[0012] In the method according to the first aspect of this disclosure, optionally, the predetermined cooling cycle temperature is not higher than 0°C. In this case, when the cleaning solvent is heated and evaporated and rises to the reflux condenser, by setting the predetermined cooling cycle temperature to not higher than 0°C, the condensation and reflux effect of the cleaning solvent vapor can be improved. Thus, the cleaning solvent vapor can form droplets after being cooled and re-enter the reaction vessel, thereby improving the cleaning efficiency and cleaning effect of the reaction vessel.

[0013] In the method according to the first aspect of this disclosure, optionally, the reflux condenser is a serpentine reflux condenser. In this case, when the cleaning solvent is heated and evaporated and rises to the serpentine reflux condenser, the vapor of the cleaning solvent, upon contact with the serpentine reflux condenser, can form small droplets inside the serpentine reflux condenser, gradually gather into droplets, and eventually fall back into the reaction vessel. This helps to increase the reflux flow rate of the cleaning solvent vapor, thereby improving the cleaning efficiency and cleaning effect on the reaction vessel.

[0014] In the method according to the first aspect of this disclosure, optionally, the reaction vessel is selected from one of a conical flask, a two-necked flask, or a three-necked flask, and the types of reaction vessels may be the same or different. This allows for the addition of a cleaning solvent to the reaction vessel, and the installation of a reflux condenser at the opening of the reaction vessel, thereby facilitating cleaning of the reaction vessel.

[0015] In the method according to the first aspect of this disclosure, optionally, after obtaining the mixture, the mixture is removed from the reaction vessel while it is still hot. In this case, by removing the mixture from the reaction vessel while it is still hot, the possibility of incomplete cleaning due to the precipitation of reaction residues in the mixture caused by the decrease in temperature can be effectively reduced; in other words, it can help improve the cleaning effect on the reaction vessel.

[0016] In the method according to the first aspect of this disclosure, optionally, obtaining the mass of the reaction residue includes the following steps: weighing the reaction vessel before preparing lactide to obtain the mass of the reaction vessel; weighing the reaction vessel containing the reaction residue after preparing lactide to obtain the total mass; and subtracting the mass of the reaction vessel from the total mass to obtain the mass of the reaction residue. In this case, by obtaining the mass of the reaction residue, it is convenient to determine the volume of cleaning solvent added to the reaction vessel.

[0017] The second aspect of this disclosure provides a cleaning solvent for cleaning a reaction vessel used in the preparation of lactide. The reaction vessel has an opening and its inner wall is adhered with reaction residues left after the preparation of lactide. These reaction residues include polylactic acid oligomers. The cleaning solvent is a potassium hydroxide solution with a concentration of 0.1 mol / L to 1 mol / L. The ratio of the volume (in L) of the cleaning solvent to the mass (in kg) of the reaction residues inside the reaction vessel is not less than 1. When cleaning the reaction vessel with the cleaning solvent, a reflux condenser is installed at the opening of the reaction vessel for condensation. The reaction vessel is heated until the cleaning solvent inside the reaction vessel reaches a predetermined heating temperature and is maintained for a predetermined heating time to obtain a mixture containing the reaction residues. The mixture is then removed from the reaction vessel to obtain a cleaned reaction vessel. The predetermined heating temperature is not less than 150°C. In this second aspect of the disclosure, by using this cleaning solvent to clean the reaction vessel, a clean reaction vessel can be obtained.

[0018] According to this disclosure, a method for cleaning multiple reaction vessels for preparing lactide simultaneously, which is simple, low-cost, and highly efficient, and a cleaning solvent for cleaning reaction vessels for preparing lactide are provided. Attached Figure Description

[0019] Figure 1 This is a flowchart illustrating the preparation of lactide as described in the examples of this disclosure.

[0020] Figure 2 This is a flowchart illustrating a method for simultaneously cleaning multiple reaction vessels used in the preparation of lactide, as described in the examples of this disclosure.

[0021] Figure 3 This is a schematic diagram illustrating a condensation reflux apparatus as described in the examples of this disclosure.

[0022] Explanation of reference numerals in the attached figures:

[0023] 1…Reaction vessel, 2…Reflux condenser, 20…Reflux condenser tube, 21…Channel, 22…Fourth opening, 30…Condenser. Detailed Implementation

[0024] All references cited in this disclosure are incorporated herein by reference in their entirety, as fully illustrated. Unless otherwise defined, the technical and scientific terms used in this disclosure have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure pertains.

[0025] Hereinafter, preferred embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. In the following description, the same reference numerals will be used for the same components, and repeated descriptions will be omitted. Furthermore, the drawings are merely schematic diagrams, and the proportions of the components or the shapes of the components may differ from actual figures.

[0026] It should be noted that the terms "comprising" and "having" and any variations thereof in this invention, such as a process, method, system, product, or device that includes or has a series of steps or units, are not necessarily limited to those steps or units that are explicitly listed, but may include or have other steps or units that are not explicitly listed or that are inherent to such processes, methods, products, or devices.

[0027] The first aspect of this disclosure relates to a method for simultaneously cleaning multiple reaction vessels used in the preparation of lactide. This cleaning method is simple, low-cost, and highly efficient. Furthermore, it ensures that reaction vessels free of reactive residues are cleaned using this method. This method for simultaneously cleaning multiple reaction vessels used in the preparation of lactide can be simply referred to as a "cleaning method," and may also be called a method for cleaning reaction vessels used in the preparation of lactide, a method for cleaning reaction vessels, or a method for simultaneously cleaning multiple polylactic acid polymerization reactors, etc.

[0028] The reaction vessel cleaned by the method of this disclosure, free of reactive residue, can be recovered and reused. For example, the cleaned reaction vessel can be used in the laboratory or reused for the preparation of lactide. The cleaning method of this disclosure can also be used to clean polylactic acid polymerization apparatus. That is, the cleaning method of this disclosure can be used to clean containers containing polylactic acid oligomers.

[0029] The method for cleaning multiple reaction vessels for preparing lactide, which relates to the first aspect of this disclosure, will be described below with reference to the accompanying drawings.

[0030] Figure 1 This is a flowchart illustrating the preparation of lactide as described in the examples of this disclosure.

[0031] In this embodiment, the preparation of lactide may include: preparing a lactic acid raw material (step S11); preparing an amphoteric metal oxide as a catalyst (step S12); adding the catalyst to the lactic acid raw material and polymerizing the lactic acid raw material to obtain a polylactic acid oligomer (step S13); and pyrolyzing the polylactic acid oligomer to obtain lactide (step S14) (see...). Figure 1 In this process, the order of steps S11 and S12 is not critical. For example, step S11 can be performed before step S12, or step S12 can be performed before step S11, or steps S11 and S12 can be performed simultaneously. In this case, in step S14, the polylactic acid oligomer usually cannot be completely decomposed into lactide. The polylactic acid oligomer that cannot be decomposed into lactide, as well as the catalyst that has cooled and solidified, may adhere to the inner wall of the reaction vessel and be difficult to pour out directly, making the reaction vessel unusable. The substance adhering to the inner wall of the reaction vessel is called the reaction residue. That is to say, the reaction residue may include polylactic acid oligomer.

[0032] It should be noted that the reaction vessel for preparing lactide disclosed herein can be used not only to prepare lactide by the above method, but also by other methods that may produce polylactic acid oligomers.

[0033] Figure 2 This is a flowchart illustrating a method for simultaneously cleaning multiple reaction vessels used in the preparation of lactide, as described in the examples of this disclosure.

[0034] In this embodiment, the method for simultaneously cleaning multiple reaction vessels for preparing lactide may include: preparing a cleaning solvent (step S100); adding the cleaning solvent to each reaction vessel respectively (step S200); setting a reflux condenser at the opening of the reaction vessel, connecting the reflux condenser in series with a condenser (step S300); turning on the condenser and setting a predetermined cooling cycle temperature for condensation, heating the reaction vessel until the cleaning solvent reaches the predetermined heating temperature, and maintaining the heating for a predetermined time to obtain a mixture containing dissolved reaction residues (step S400); removing the mixture from the reaction vessel to obtain a cleaned reaction vessel (step S500).

[0035] In this process, the reaction residues are dissolved in the cleaning solvent, and then the mixture containing the dissolved reaction residues is removed, thereby cleaning the reaction vessel for preparing lactide. In step S200, by adding the cleaning solvent to each reaction vessel, multiple reaction vessels for preparing lactide can be cleaned simultaneously. In step S300, by installing reflux condensers at the openings of the reaction vessels and connecting them in series to a condenser, it is convenient to simultaneously perform reflux condensation on the reactants in multiple reaction vessels, thereby improving the cleaning efficiency of the reaction vessels and the utilization rate of the equipment. In step S400, by heating the reaction vessels until the cleaning solvent reaches a predetermined heating temperature and maintaining the heating for a predetermined time, the dissolution rate and solubility of the reaction residues in the cleaning solvent can be increased, thereby improving the cleaning effect of the reaction vessels.

[0036] In this disclosure, the reaction vessel for preparing lactide can be simply referred to as the reaction vessel, and the reflux condenser can be simply referred to as the condenser.

[0037] In some examples, the cleaning solvent in step S100 can be a potassium hydroxide solution. In some examples, the concentration of the potassium hydroxide solution can be from 0.1 mol / L to 1 mol / L. For example, the concentration of the potassium hydroxide solution can be 0.1 mol / L, 0.2 mol / L, 0.3 mol / L, 0.4 mol / L, 0.5 mol / L, 0.6 mol / L, 0.7 mol / L, 0.8 mol / L, 0.9 mol / L, or 1 mol / L. In this case, by using a potassium hydroxide solution as the cleaning solvent and configuring its concentration to be from 0.1 mol / L to 1 mol / L, it is possible to promote the dissolution of reaction residues in the alkaline cleaning solvent, thereby improving the cleaning effect on the reaction vessel.

[0038] In some examples

[0039] The cleaning solvent can be used to clean containers used in laboratory preparations of lactide. In some examples, the cleaning solvent can also be used to clean other containers containing polylactic acid oligomers.

[0040] In some examples, in step S200, the cleaning solvent can be added to each reaction vessel separately. This allows multiple reaction vessels to be cleaned.

[0041] In some examples, in step S200, the ratio of the volume (in L) of the cleaning solvent in each reaction vessel to the mass (in kg) of the reaction residue in each reaction vessel can be no less than 1. In other words, the volume-to-mass ratio of the cleaning solvent to the reaction residue can be no less than 1 L: 1 kg. In this case, it is beneficial for the reaction residue to react fully with the cleaning solvent, thereby facilitating the dissolution of the reaction residue. It is understood that when cleaning the reaction vessel, the more cleaning solvent used, the more thoroughly the reaction vessel can be cleaned. In this disclosure, by using a condenser in conjunction with a specific cleaning solvent, the reaction vessel can be cleaned effectively when the volume-to-mass ratio of the cleaning solvent to the reaction residue is no less than 1 L: 1 kg, thereby reducing cleaning costs.

[0042] In some examples, in step S200, the volume-to-mass ratio of the cleaning solvent to the reaction residue can be 1L:1kg, 1.5L:1kg, 2L:1kg, 2.5L:1kg, 3L:1kg, 3.5L:1kg, 4L:1kg, 4.5L:1kg, or 5L:1kg.

[0043] In some examples, obtaining the mass of the reaction residue may include the following steps: weighing the reaction vessel before the reaction (i.e., before preparing lactide) to obtain the mass of the reaction vessel; weighing the reaction vessel containing the reaction residue after the reaction (i.e., after preparing lactide and emptying the lactide from the vessel) to obtain the total mass; and subtracting the mass of the reaction vessel from the total mass to obtain the mass of the reaction residue. In this case, the mass of the reaction residue can be obtained, thereby determining the volume of the cleaning solvent added to the reaction vessel.

[0044] In some examples, in step S200, preferably, the number of reaction vessels can be two to four. For example, the number of reaction vessels can be two, three, or four. In this case, two to four reaction vessels can be cleaned simultaneously, thereby improving cleaning efficiency.

[0045] In some examples, in step S200, the reaction vessel can be selected from a conical flask, a two-necked flask, or a three-necked flask, and the types of reaction vessels can be the same or different. This facilitates the addition of cleaning solvent to the reaction vessel and the installation of a reflux condenser at the opening of the reaction vessel, thereby facilitating cleaning. Of course, the cleaning method of this disclosure can also be used to clean other containers with reaction residues; only a few commonly used containers in experiments are listed here as examples and should not be construed as limiting. For example, in the preparation of lactide, different types of reactants are usually added to the reaction vessel; therefore, a three-necked flask is generally used as the reaction vessel for preparing lactide.

[0046] In some examples, in step S300, a reflux condenser can be installed at the opening of each reaction vessel. In this case, when the reaction vessel is heated subsequently, the vapor of the cleaning solvent that evaporates due to heat can be condensed and refluxed back into the reaction vessel to participate in the reaction. This saves on the amount of cleaning solvent used, and the reaction vessel can be cleaned with a predetermined proportion of cleaning solvent, while also reducing the cost of cleaning the reaction vessel.

[0047] In some examples, the reflux condenser tubes can be connected in series. These series-connected reflux condenser tubes can then be connected to a condenser. In this case, when cleaning the reaction vessels, a single condenser can simultaneously supply the condensate needed for reflux to multiple reaction vessels, improving both the efficiency of cleaning multiple reaction vessels and the utilization rate of the condenser. In other words, by configuring a single condenser, multiple reaction vessels can be cleaned simultaneously.

[0048] In some examples, the reflux condenser may have a channel for the movement of cleaning solvent vapor between the inner wall of its outer contour and the outer wall of the inner tube. In this case, by allowing the condensate to flow in the inner tube, the temperature of the space within the channel can be reduced. When the cleaning solvent vapor enters the lower-temperature channel, it is beneficial for the cleaning solvent vapor to condense into small droplets upon contact with the condenser, and further condense and converge into droplets on the outer wall of the inner tube and the inner wall of the outer contour of the reflux condenser, falling into the reaction vessel. This helps to increase the reflux flow rate of the cleaning solvent vapor, thereby improving the cleaning efficiency and cleaning effect on the reaction vessel. In some examples, in step S300, the reflux condenser may be a serpentine reflux condenser. In this configuration, the inner tube of the serpentine reflux condenser is coiled in a serpentine shape. This coiled inner tube has a large surface area exposed within the channel, which helps to rapidly reduce the temperature of the space within the channel as the condensate flows through it. Furthermore, when the vapor of the cleaning solvent enters the cooler channel and condenses into small droplets, these droplets gradually accumulate on the outer wall of the cooler inner tube. When the droplets accumulate to a certain amount, they slide down the outer wall of the coiled inner tube under their own gravity, continuously accumulating droplets to form a liquid flow that eventually flows downwards into the reaction vessel. This improves the reflux speed and flow rate of the cleaning solvent vapor, thereby enhancing the cleaning efficiency and effectiveness of the reaction vessel.

[0049] Figure 3 This is a schematic diagram illustrating the condenser reflux apparatus 2 as described in the example of this disclosure. Figure 3In this example, taking four three-necked flasks as the reaction vessel 1 and a serpentine reflux condenser 20 as the exemplary reflux condenser 20, the reaction vessel 1, the reflux condenser 2, and their combined function are illustrated. Figure 3 The arrows in the diagram schematically indicate the direction of condensate movement.

[0050] In such Figure 3 In the example shown, each reflux condenser 20 can be located in one of the openings of each three-necked flask (e.g., Figure 3 The reflux condenser 20 is connected in series with the condenser 30 via connecting pipes. During heating, the other openings of the three-necked flask not connected to the reflux condenser 20 can be closed, allowing the cleaning solvent vapor to move from the openings connected to the reflux condenser 20 into the reflux condenser 20. The end of the reflux condenser 20 furthest from the three-necked flask has an opening (hereinafter referred to as the fourth opening 22). When cleaning the reaction vessel 1, the reflux condenser 20 can be opened through the fourth opening 22. With the connection to the outside, when the cleaning solvent moves upward due to heating and evaporation, even if the vapor of the cleaning solvent cannot be completely condensed and refluxed in the channel 21 of the reflux condenser 20, the vapor of the cleaning solvent can still escape to the outside through the fourth opening 22. This helps to keep the gas pressure in the reaction vessel 1 and the reflux condenser 20 in balance with the outside gas pressure, effectively preventing the reaction vessel 1 and / or the reflux condenser 20 from rupturing due to excessive internal gas pressure, thereby improving the safety of the cleaning process.

[0051] In some examples, in step 400, the predetermined cooling cycle temperature can be set to no higher than 0°C. For example, the predetermined cooling cycle temperature can be 0°C, -1°C, -2°C, -3°C, -4°C, or -5°C, etc. In this case, when the cleaning solvent is heated and evaporated and rises to the reflux condenser, setting the predetermined cooling cycle temperature to no higher than 0°C can improve the condensation and reflux effect of the cleaning solvent vapor, thereby increasing the reflux flow rate of the cleaning solvent vapor.

[0052] In some examples, the reaction vessel for preparing lactide can also be cleaned without using a reflux condenser. In this case, since the cleaning solvent evaporates due to heating, the reaction vessel can be thoroughly cleaned by adding more cleaning solvent or adding it multiple times during the cleaning process to maintain a suitable amount of cleaning solvent inside the vessel at all times.

[0053] In some examples, the cleaning method of this disclosure can also be used to clean a single reaction vessel. In this case, by providing a reflux condenser at the opening of the reaction vessel, the vapor of the subsequently heated and evaporated cleaning solvent can be refluxed back into the reaction vessel to participate in the reaction.

[0054] In some examples, the cleaning method of this disclosure can also clean more than four reaction vessels simultaneously. For example, five reaction vessels can be cleaned at the same time. Since the temperature of the condensate in the reflux condenser rises as it moves through the condenser, when the condensate flows through a relatively later condenser, such as the fifth condenser, the increased temperature of the condensate in that condenser may prevent the cleaning solvent vapor in the fifth reaction vessel from achieving the desired condensation effect. This causes some of the cleaning solvent vapor to escape through the condenser, affecting the cleaning effect on that reaction vessel. In this case, when cleaning more than four reaction vessels is required, the condensation and reflux effect of the cleaning solvent vapor can be improved by setting a lower cooling circulation temperature. For example, the cooling circulation temperature can be set to -5°C. This improves the condensation and reflux effect of the cleaning solvent vapor, thereby improving the cleaning efficiency and effectiveness of the reaction vessels.

[0055] In some examples, in step S400, the predetermined heating temperature can be configured to be no less than 150°C. For example, the predetermined heating temperature can be 150°C, 160°C, 170°C, 180°C, or 190°C. In some examples, preferably, the predetermined heating temperature can be between 150°C and 160°C. In some examples, the predetermined heating time can be between 6 hours and 24 hours. For example, the predetermined heating time can be 6 hours, 8 hours, 10 hours, 12 hours, 14 hours, 16 hours, 18 hours, 20 hours, 22 hours, or 24 hours. In this case, by setting a specific heating temperature and heating time, it is beneficial for the reaction residue to react fully with the cleaning solvent, thereby facilitating the full dissolution of the reaction residue in the cleaning solvent and improving the cleaning effect on the reaction vessel. However, the examples disclosed herein are not limited to this. In other examples, the predetermined heating temperature can be configured to be below 150°C, and the cleaning effect can be improved by extending the predetermined heating time. For example, the predetermined heating temperature can be 140°C, and the predetermined heating time can be 48 hours.

[0056] In some examples, in step S400, multiple reaction vessels can be heated simultaneously using an oil bath. In this case, by placing the reaction vessels in the heat-conducting oil, the bottom area of ​​the reaction vessels can be heated uniformly, which facilitates the complete dissolution of reaction residues in the cleaning solvent, thereby improving the cleaning effect of the reaction vessels.

[0057] In some examples, in step S500, after the reaction residue has been fully dissolved in the cleaning solvent, the condenser can be removed from the opening of the reaction vessel, and the mixture in the reaction vessel can be poured out.

[0058] In some examples, in step S500, the mixture can be removed from the reaction vessel while it is still hot. In this case, removing the mixture from the reaction vessel while it is still hot can effectively reduce the possibility of incomplete cleaning caused by the precipitation of reaction residues in the mixture due to the decrease in temperature, thereby improving the cleaning effect on the reaction vessel.

[0059] In some examples, in step S500, after the mixture is removed from the reaction vessel, the reaction vessel can be rinsed multiple times with water. This improves the cleanliness of the interior of the reaction vessel.

[0060] In summary, the first aspect of this disclosure provides a method that is simple, low-cost, and highly efficient for simultaneously cleaning multiple reaction vessels used in the preparation of lactide. The removal rate of reaction residues in the cleaned reaction vessels is 100%, and the cleaned reaction vessels are free of reaction residues, allowing them to be recycled and reused (e.g., for laboratory use or for the preparation of lactide again).

[0061] The second aspect of this disclosure relates to a cleaning solvent for cleaning reaction vessels used in the preparation of lactide. In this second aspect, by using this cleaning solvent to clean the reaction vessel, a cleaned reaction vessel can be obtained. The cleaning solvent involved in this second aspect is consistent with the cleaning solvent in the cleaning method of the first aspect of this disclosure; a detailed description of the cleaning solvent can be found above in the description of the cleaning solvent in the cleaning method, and will not be repeated here.

[0062] When cleaning a reaction vessel containing reaction residues using the cleaning solvent described in the second aspect of this disclosure, the cleaning method described in the first aspect of this disclosure can also be used. Specifically, a reflux condenser can be installed at the opening of the reaction vessel for condensation. The reaction vessel is heated until the cleaning solvent inside reaches a predetermined heating temperature and maintained for a predetermined heating time to obtain a mixture containing dissolved reaction residues. The mixture is then removed from the reaction vessel to obtain a cleaned reaction vessel. The predetermined heating temperature is not lower than 150°C. The various parameters, proportions, and settings are as described above in the cleaning method section and will not be repeated here.

[0063] In summary, in the second aspect of this disclosure, a cleaning solvent can be provided for cleaning reaction vessels used in the preparation of lactide. After cleaning, the reaction vessel is free of reactive residues and can be recycled and reused (e.g., for laboratory use or for the preparation of lactide again).

[0064] The cleaning method provided in this disclosure will be described in detail below with reference to embodiments and comparative examples, but these should not be construed as limiting the scope of protection of this disclosure.

[0065] [Example]

[0066] First, the reaction vessel was weighed to obtain its mass before preparing lactide.

[0067] Secondly, lactide is prepared by the following steps: preparing lactic acid raw material; preparing an amphoteric metal oxide as a catalyst; adding the lactic acid raw material and the catalyst to the reaction vessel and polymerizing the lactic acid raw material to obtain polylactic acid oligomer; and pyrolyzing the polylactic acid oligomer to obtain lactide.

[0068] Next, the prepared lactide is removed from the reaction vessel, and the reaction vessel containing the reaction residue is weighed to obtain the total mass. The mass of the reaction vessel is then subtracted from the total mass to obtain the mass of the reaction residue.

[0069] Therefore, according to Table 1, the cleaning solvents of Examples 1 to 12 were prepared.

[0070] Then, the cleaning solvent is added to the reaction vessel in the proportions shown in Table 1.

[0071] Then, a reflux condenser is installed at the opening of the reaction vessel in each of the embodiments from Example 1 to Example 7, and the reflux condenser is connected to the condenser; a reflux condenser is installed at the opening of each of the four reaction vessels in each of the embodiments from Example 8 to Example 12, and the reflux condensers are connected in series and then connected to the condenser.

[0072] Next, according to Table 1, the condenser is turned on and the predetermined cooling cycle temperature is set for condensation. Multiple reaction vessels are heated until the cleaning solvent inside each reaction vessel reaches the predetermined heating temperature and is maintained for a predetermined heating time to obtain a mixture containing dissolved reaction residues.

[0073] Finally, the reflux condenser was removed from the opening of each reaction vessel, and the mixture was removed from the reaction vessel to obtain the cleaned reaction vessels of Examples 1 to 12.

[0074] Table 1

[0075]

[0076] [Comparative Example]

[0077] First, the mass of the reaction vessel was obtained by weighing it using an electronic scale before preparing lactide.

[0078] Secondly, lactide is prepared by the following steps: preparing lactic acid raw material; preparing an amphoteric metal oxide as a catalyst; adding the lactic acid raw material and the catalyst to the reaction vessel and polymerizing the lactic acid raw material to obtain polylactic acid oligomer; and pyrolyzing the polylactic acid oligomer to obtain lactide.

[0079] Next, the prepared lactide is removed from the reaction vessel, and the reaction vessel containing the reaction residue is weighed using an electronic scale to obtain the total mass. The mass of the reaction vessel is then subtracted from the total mass to obtain the mass of the reaction residue.

[0080] Therefore, according to Table 2, the cleaning solvents for Comparative Examples 1 to 27 were prepared.

[0081] Then, according to Table 2, the cleaning solvent was added to each reaction vessel in a ratio of not less than 1: the volume of the cleaning solvent in each reaction vessel (in L) to the mass of the reaction residue in the reaction vessel (in kg).

[0082] Then, a reflux condenser was installed at the opening of the reaction vessel of each of the comparative examples 1 to 6 and 11 to 27, and the reflux condenser was connected to the condenser; a reflux condenser was installed at the opening of the four reaction vessels of each of the comparative examples 7 to 10, and the reflux condensers were connected in series and then connected to the condenser.

[0083] Next, the condenser is turned on, and the predetermined cooling cycle temperature is set according to Table 2 for condensation. According to Table 2, multiple reaction vessels are heated until the cleaning solvent inside each reaction vessel reaches the predetermined heating temperature (the predetermined heating temperature is room temperature, which means that the reaction vessel is placed in a room temperature environment of 25°C), and the predetermined heating time is maintained to obtain a mixture containing dissolved reaction residues.

[0084] Finally, the reflux condenser was removed from the opening of each reaction vessel, and the mixture was removed from the reaction vessel to obtain the cleaned reaction vessels of Comparative Examples 1 to 27.

[0085] Table 2

[0086]

[0087] During the above operations, the reflux of the cleaning solvent in the reflux condenser tubes of each embodiment (Examples 1 to 12) and each comparative example (Comparative Examples 1 to 27) was observed and recorded. In the embodiments and comparative examples with four cleaning containers, the observation of the reflux of the cleaning solvent refers to observing the reflux of the cleaning solvent in the last of the four series-connected reflux condenser tubes. "Complete reflux" means that during the cleaning process, droplets condensing upon cooling were observed only in approximately one-third of the lower part of the reflux condenser tube; "large reflux" means that during the cleaning process, droplets condensing upon cooling were observed only in approximately two-thirds of the lower part of the reflux condenser tube; and "small reflux" means that during the cleaning process, droplets condensing upon cooling were observed in the entire area of ​​the reflux condenser tube. The recorded results are shown in Table 3. The removal rate of reaction residues in the cleaned reaction containers was calculated as follows: The total mass of the cleaned reaction containers in each embodiment and comparative example was obtained using an electronic scale, and the removal rate of reaction residues was calculated based on the weighing results, as shown in Table 3. The formula for calculating the removal rate of reaction residues is: Removal rate = (Mass of reaction residues - Mass of reaction residues after cleaning) / Mass of reaction residues × 100%. When calculating the removal rate of reaction residues in each embodiment and comparative example with four cleaned containers, the average removal rate of reaction residues in the four reaction containers was taken as the removal rate of reaction residues in each embodiment and comparative example.

[0088] It should be noted that, unless otherwise specified, all reagents and instruments used in the embodiments, comparative examples, and the above measurement processes disclosed herein are commercially available products.

[0089] Table 3

[0090] Reflux of cleaning solvent Removal rate of reaction residue (%) Example 1 All recirculation 100 Example 2 All recirculation 100 Example 3 All recirculation 100 Example 4 All recirculation 100 Example 5 All recirculation 100 Example 6 All recirculation 100 Example 7 All recirculation 100 Example 8 All recirculation 100 Example 9 All recirculation 100 Example 10 All recirculation 100 Example 11 All recirculation 100 Example 12 All recirculation 100 Comparative Example 1 \ 2 Comparative Example 2 All recirculation 74 Comparative Example 3 All recirculation 91 Comparative Example 4 Large-scale reflux 96 Comparative Example 5 All recirculation 82 Comparative Example 6 Large-scale reflux 92 Comparative Example 7 All recirculation 67 Comparative Example 8 All recirculation 88 Comparative Example 9 Large-scale reflux 85 Comparative Example 10 Small amount of reflux 77 Comparative Example 11 All recirculation 55 Comparative Example 12 Large-scale reflux 41 Comparative Example 13 \ 2 Comparative Example 14 All recirculation 30 Comparative Example 15 All recirculation 86 Comparative Example 16 Large-scale reflux 72 Comparative Example 17 \ 0 Comparative Example 18 All recirculation 2 Comparative Example 19 \ 5 Comparative Example 20 Large-scale reflux 24 Comparative Example 21 Small amount of reflux 16 Comparative Example 22 \ 10 Comparative Example 23 Large-scale reflux 67 Comparative Example 24 Small amount of reflux 35 Comparative Example 25 \ 11 Comparative Example 26 Large-scale reflux 70 Comparative Example 27 Small amount of reflux 43

[0091] As can be seen from Table 3, the removal rate of reaction residues in each embodiment (Example 1 to Example 12) was 100%.

[0092] In particular, in the preferred embodiment, the predetermined heating time for Examples 5, 6, 7, 11, and 12 is 6 hours, and the removal rate of reaction residue is 100%.

[0093] In particular, in the preferred embodiments, Examples 8 to 12 can clean four reaction vessels simultaneously, and the removal rate of reaction residues is 100%.

[0094] The removal rate of reaction residues in the reaction vessel cleaned in Example 3 was 100%. The main reason is that when cleaning a single reaction vessel, under the condition of a predetermined heating temperature of 170°C, the vapor of the cleaning solvent can be completely refluxed in the condenser reflux tube. After a predetermined heating time of 12 hours, the reaction residues can be completely dissolved in a 0.1 mol / L potassium hydroxide solution.

[0095] The removal rate of reaction residues in the reaction vessel cleaned in Example 4 was 100%. The main reason is that although the dissolution rate of reaction residues in 1 mol / L potassium hydroxide solution was lower at a predetermined heating temperature of 140°C compared to a predetermined heating temperature of 150°C, the reaction residues were completely dissolved after a predetermined heating time of 12 hours.

[0096] The removal rate of reaction residues in the reaction vessel cleaned in Comparative Example 1 was only 2%, mainly because the predetermined heating temperature was low. At room temperature (25°C), the reaction residues had very low solubility in 0.1 mol / L potassium hydroxide solution.

[0097] The removal rates of reaction residues in the reaction vessels cleaned in Comparative Examples 2 and 3 were 74% and 91%, respectively. The main reason for this was the low predetermined heating temperature. Under the predetermined heating temperature conditions of 130℃ and 140℃, the dissolution rate of the reaction residues in 0.1 mol / L potassium hydroxide solution was low. After the predetermined heating time of 24 h, the reaction residues could not be completely dissolved.

[0098] The removal rate of reaction residues in the reaction vessel cleaned in Comparative Example 4 was 96%. The main reason for this was the low predetermined heating temperature. Under the predetermined heating temperature of 130°C, the dissolution rate of the reaction residues in the 1 mol / L potassium hydroxide solution was low. After the predetermined heating time of 24 h, the reaction residues could not be completely dissolved.

[0099] The removal rates of reaction residues in the reaction vessels cleaned by Comparative Examples 5 and 6 were 82% and 92%, respectively. The main reason for this was that the predetermined heating temperature was relatively high. Under the predetermined heating temperature of 180°C, the cleaning solvent in the reaction vessel evaporated rapidly. A large amount of cleaning solvent vapor was generated in a short time. It could not be completely refluxed in the condenser reflux tube and could only be refluxed in a small amount. As a result, the amount of cleaning solvent in the reaction vessel was reduced and insufficient to completely dissolve the reaction residues.

[0100] The removal rates of reaction residues in the reaction vessels cleaned by Comparative Examples 7 and 8 were 67% and 88%, respectively. The main reason for this was the low predetermined heating temperature. Under the predetermined heating temperature conditions of 130°C and 140°C, the degradation rate of the reaction residues in the 0.1 mol / L potassium hydroxide solution was low, and the reaction residues could not be completely dissolved after the predetermined heating time of 24 h.

[0101] The removal rates of reaction residues in the reaction vessels cleaned in Comparative Examples 9 and 10 were 85% and 77%, respectively. The main reason for this was that the predetermined heating temperature was high and the number of reaction vessels cleaned was large. Under the predetermined heating temperature conditions of 170°C and 180°C, the cleaning solvent in the reaction vessels evaporated quickly. Furthermore, the condensate was heated after entering the series-connected reflux condenser due to the heat transfer effect of the cleaning solvent vapor. The condensate's condensation effect on the cleaning solvent was weakened after entering the reflux condenser located at the end of the series connection. As a result, a large amount of cleaning solvent vapor generated in a short time could not be completely refluxed in the series-connected reflux condenser, but only a small amount could be refluxed. This reduced the amount of cleaning solvent in the reaction vessels, which was insufficient to completely dissolve the reaction residues.

[0102] The removal rate of residual substances in the reaction vessel cleaned in Comparative Example 11 was 55%. The main reason was that the concentration of potassium hydroxide solution used as the cleaning solvent was low. Under the predetermined heating temperature of 150°C, the solubility of the reaction residue in 0.01 mol / L potassium hydroxide solution was low and insufficient to completely dissolve the reaction residue.

[0103] The removal rate of residual substances in the reaction vessel cleaned in Comparative Example 15 was 86%. The main reason is that the hydrochloric acid solution used as the cleaning solvent was not very effective in dissolving the reaction residues. Under the predetermined heating temperature of 150°C, the solubility of the reaction residues in 0.1 mol / L hydrochloric acid solution was low and insufficient to completely dissolve the reaction residues.

[0104] The removal rates of residual substances in the reaction vessels cleaned by Comparative Examples 20, 23, and 26 were 24%, 67%, and 70%, respectively. The main reason is that the potassium hydroxide ethanol solution, dichloromethane, and trichloromethane used as cleaning solvents were not very effective in dissolving the reaction residues. Under the predetermined heating temperature of 100°C, the dissolution rate of the reaction residues in 0.1 mol / L potassium hydroxide ethanol solution, dichloromethane, and trichloromethane was low. After the predetermined heating time of 24 h, the reaction residues could not be completely dissolved.

[0105] The removal rates of residual substances in the reaction vessels cleaned by Comparative Examples 21, 24, and 27 were 16%, 35%, and 43%, respectively. The main reason is that potassium hydroxide ethanol solution, dichloromethane, and trichloromethane are relatively volatile. As cleaning solvents, potassium hydroxide ethanol solution, dichloromethane, and trichloromethane evaporate quickly at the predetermined heating temperature of 150°C. A large amount of cleaning solvent vapor is generated in a short time. It cannot be completely refluxed in the condenser reflux tube, but only a small amount can be refluxed. As a result, the amount of cleaning solvent in the reaction vessel is reduced and is insufficient to completely dissolve the reaction residue.

[0106] In summary, the reaction vessels for preparing lactide obtained through the cleaning methods in each embodiment (Examples 1 to 12) showed no residual reaction substances, the cleaning methods were simple, and multiple reaction vessels for preparing lactide could be cleaned simultaneously in Examples 8 to 12, resulting in high efficiency. In contrast, the methods for cleaning the reaction vessels for preparing lactide in the comparative examples (Comparative Examples 1 to 27) could not simultaneously achieve the effects of the cleaning methods for the reaction vessels for preparing lactide in the above embodiments (Examples 1 to 12).

[0107] While the present disclosure has been specifically described above in conjunction with the accompanying drawings and examples, it is to be understood that the foregoing description does not limit the present disclosure in any way. Those skilled in the art can make modifications and variations to the present disclosure as needed without departing from its essential spirit and scope, and all such modifications and variations shall fall within the scope of the present disclosure.

Claims

1. A method for simultaneously cleaning multiple containers, characterized in that, The container has an opening and its inner wall is adhered with reaction residues including polylactic acid oligomers; the method includes: The cleaning solvent is added to each container respectively, wherein the cleaning solvent is a potassium hydroxide solution with a concentration of 0.1 mol / L to 1 mol / L, and the volume-to-mass ratio of the cleaning solvent added to each container to the reaction residue in each container is not less than 1 L: 1 kg. Each container is connected to a reflux condenser, wherein a reflux condenser is provided at the opening of each container. The reflux condenser has a channel for the vapor of the cleaning solvent to move between the inner wall of its outer contour and the outer wall of the inner tube. The reflux condenser includes a condenser, and each reflux condenser is connected in series to the condenser. A predetermined cooling cycle temperature is set for condensation, and the plurality of containers are heated and maintained for a predetermined heating time to obtain a mixture containing the reaction residue. The vapor of the cleaning solvent evaporated by heating is re-entered into each container to participate in the reaction via condensation reflux. The predetermined heating temperature for heating the plurality of containers is 150°C to 160°C, and the predetermined heating time is 6 hours to 24 hours; or the predetermined heating temperature for heating the plurality of containers is 140°C, and the predetermined heating time is 48 hours. The mixture is removed from each container to obtain cleaned containers.

2. The method according to claim 1, characterized in that, After the mixture is removed from each container, each container is rinsed multiple times with water.

3. The method according to claim 1, characterized in that, The end of the reflux condenser that is relatively far from the container has an opening, and during heating, the reflux condenser is connected to the outside through the opening of the reflux condenser.

4. The method according to claim 1, characterized in that, The predetermined cooling cycle temperature is not higher than 0°C.

5. The method according to claim 1 or 4, characterized in that, When cleaning more than four of the containers, the predetermined cooling cycle temperature is set to -5°C.

6. The method according to claim 1, characterized in that, After the reaction residue has been fully dissolved in the cleaning solvent, the mixture is removed from each container while it is still hot.

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